JPH07281218A - Optical waveguide that is epitaxially grown on semiconductorfor upgrade conversion - Google Patents

Abstract

PURPOSE: To enable growing a diode laser, up-conversion light source, photodetector, etc., on the same chip by adopting a multilayered structure, consisting of a substrate, a buffer layer and an epitaxial fluoride outer film layer exhibiting the up-conversion excited by red or IR irradiation. CONSTITUTION: The multilayered structure 10 consists of the single crystal semiconductor substrate 11, the epitaxial buffer fluoride layer 13 and the up- conversion fluoride film 15 epitaxially growing on the substrate 11 and forming a waveguide, together with the buffer layer 13 thereunder. The buffer layer 13 is a single crystal film which hinders the reaction between the fluoride film on the outer side, and the semiconductor substrate thereunder is stable with respect to the fluoride film on the outer side and the semiconductor substrate thereunder at an elevated temp. and has the same rotational symmetry and partial lattice constant as those of the substrate, with respect to the surface normal. The film is an optical film which acts as a seed for the epitaxial growth of the outer fluoride film, is transparent over a wide range of wavelengths and has the refractive index lower than the refractive index of the up- conversion.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a multilayer upconversion structure.

[0002]

Upconversion lasers are classified as optically pumped lasers that oscillate at frequencies higher than those used for pumping. The laser produces output in the violet to red spectral region using the infrared pump wavelengths available in III-V semiconductor lasers. These small light sources are important in optical data storage, high speed laser printers, large screen displays, and undersea communications. Commonly used materials for upconversion include BaY ₂ F ₈ doped with Er and YLiF ₄ doped with Tm. Paz-Pujalt, Hu
ng, Chwalek, Hrycin, Chatter
Jee, Richards, US Patent Application No. 08/186400, filed January 25, 1994, "A De
vice for Converting Invis
Ible and VisibleRadiation
to Visible Light And / Or
Crystal layer is disclosed in BaYYbF ₈ doped with Tm on the substrate indicating the UVRadiation "In upconversion excitation. It is GaAs and other II
It is still desirable to integrate epitaxial films of up-conversion material on IV semiconductors. Hung, A
US patent application Ser. No. 07 / 992,213 filed Dec. 7, 1992 by Gostinelli, Mir “A
Multilayer Structure Havi
ng a (111) -Oriented Buffer
"r Layer" discloses a GaAs substrate and a nonlinear optical waveguide epitaxially grown on the substrate.

[0003]

An object of the present invention is to provide an upconversion waveguide epitaxially grown on a semiconductor.

[0004]

A multi-layer structure comprising a single crystal semiconductor substrate; an epitaxial buffer layer overlaying the substrate; and an epitaxial fluoride outer film layer exhibiting upconversion excited by red or infrared radiation. Achieved by

The advantage of the multi-layered structure according to the present invention is that it is possible to grow a diode laser, an up-conversion light source, a photo-detector, and electronic components on the same chip by integrating an up-conversion film on a semiconductor substrate.
The formation of waveguides with good epitaxial quality enables high power densities over longer optical lengths.

[0006]

EXAMPLE Referring to FIG. 1, a multilayer structure 10 includes a single crystal semiconductor substrate 11 and an epitaxial buffer fluoride layer 1.
3 and an up-conversion fluoride film 15 which is epitaxially grown on the substrate 11 and forms a waveguide with the buffer layer 13 thereunder. Another embodiment according to the present invention is shown in FIG. The multilayer structure 20 is composed of single crystal Si or GaAs 21 oriented in the (100) direction and CaF ₂ 23.
And a doped up-conversion film BaYYbF that grows epitaxially on Si or GaAs and forms a waveguide with CaF _2.
8 25 and. Yet another embodiment of the present invention is shown in FIG. The multilayer structure 30 is a single crystal S oriented in the (100) direction.
i or GaAs 31, an epitaxial buffer layer of LiF 33, and a doped up-conversion film BaYYbF ₈ 35 that epitaxially grows on Si or GaAs and forms a waveguide with LiF.

The use of substrates of various types and sizes is possible with the limitation that the substrate selected is a semiconductor selected from III-V composites or IV. Preferably the substrate is GaAs, GaP, InAs, InSb and Al
a semiconductor selected from those ternary alloy composites such as _x Ga _1-x As. Preferably the Group IV substrate is S
i, Ge, and Si _x Ge _1-X , where x
Is 0 to 1.

The substrate may be undoped, lightly or heavily doped. In some applications heavily doped semiconductors are more preferred as electrodes may be formed below the buffer layer. In some applications, semiconductor parts are used as substrates 11, 21, or 31 for multilayer structures, while the remaining parts of the semiconductor wafer can be processed to form laser diodes and various electronic devices.

The buffer layer 13 of FIG. 1 must be provided as follows: 1) prevents the reaction between the outer fluoride film and the underlying semiconductor substrate, 2) the outer fluoride at elevated temperature. 3) a monocrystalline film that is stable with respect to the film and the underlying semiconductor substrate, 3) has the same rotational symmetry and sublattice constant as that of the substrate with respect to the surface normal, and 4) as a seed for epitaxial growth of the outer fluoride film. 5) is an optical film that is transparent over a wide range of wavelengths, and 6) has a lower refractive index than an up-conversion film.

This minimal property is a required property of the different possibilities of the buffer. Prior art barriers that maintain the above minimum properties may be used in the present invention. CaF
₂ , SrF ₂ , BaF ₂ , Ca _x Sr _1-X F ₂ , MgF
Various fluorides can be selected, such as ₂ , LiF (x is 0 to 1). The barrier layer 13 is epitaxially grown on the semiconductor substrate. The buffer layer 13 can be epitaxially grown by many prior art methods such as laser ablation, sputtering, electron beam evaporation, thermal evaporation, or chemical vapor deposition. When the buffer layer 13 is grown, it needs to be thick enough to prevent reaction between the substrate and the overlay film. Other considerations of film thickness must be such that the vanishing tail intensities of modes of wave propagation in the upconversion film are negligible at the substrate-buffer layer boundary to prevent guided wave loss. The preferred thickness range is 200 to 3000 nm, more preferably 500 to 2000 nm.
Is.

The overlay up-conversion film is r
It can be grown by any prior art method such as f-sputtering, electron beam evaporation, thermal evaporation, laser ablation, or metalorganic chemical vapor deposition. The overlay fluoride film shown in FIG. 1 preferably has a crystal structure compatible with the crystal structure of the underlying semiconductor substrate and exhibits a substantially upconversion effect. Membranes satisfying these two combined criteria are, for example, BaY ₂ F ₈ , B
aYYbF ₈ and YLiF ₄ . A preferred thickness range is 200 to 3000 nm, more preferably 500 to 2000 nm. The film is made of Ho, Er, Nd, Pr,
It can be doped with Tm. Experimental Details (111) GaAs wafers treated with (NH ₄ ) ₂ S _x were used as substrates for epitaxial growth of fluoride films. After prior art cleaning with organic solvent, the wafer is H ₂ SO ₄ : H ₂ O ₂ : H ₂ O = 1: 8: 500.
The solution was etched for 30 seconds, followed by a rinse with deionized water. The sample was placed in a saturated solution of (NH ₄ ) ₂ S _{x for} 3-5 minutes before mounting in the vaporizer. Following this soaking, the ammonium sulfate solution was diluted with deionized water and the sample was soaked in the diluted solution for 3-5 minutes before being dried under a stream of nitrogen. According to this method, an epitaxial film can be grown on GaAs in-situ without thermal etching or sputter cleaning.

Either CaF ₂ or LiF was deposited directly on GaAs by electron beam evaporation. Deposition process is 1x
The substrate was heated by a radiant heater made of tantalum wire at 10 ⁻⁷ Torr. Growth temperature is 40
0 ° C to 550 ° C, monitored by infrared pyrometer using published emissivity values. The deposition rate is 0.1 to 0.4 nm / s, CaF ₂ or LiF
The film thickness was about 300-500 nm.

BaYYbF₈The raw material for
BaF of raid₂, YF₃, YbF ₃, TmF₃The mole
Prepared from powders in a ratio of 1: 1: 0.99: 0.01
It was The mixed powder is under a pressure of 500 psi
Pelletized. BaYYbF doped with Tm₈
Membrane is CaF₂Or (100) GaAs covered with LiF
It is deposited by e-beam evaporation on top. Deposition is 400 °
BaYYbF performed at a temperature of C to 550 ° C₈
The film thickness was about 300-500 nm. In addition to Tm
Other elements such as Ho, Er, Nd, Pr, Tm
It can be used as a punt.

Samples are X-ray diffraction and Rutherford rear
Characterized by scattering. These techniques are well known
B. D. Element by Cullity
sof x-ray Diffraction (Ass
ion-Wesley, Reading, Massachusetts
T.) and Chu, J .; W. Mayer, M .; A. Ni
Backscattering S by colet etc.
Spectrometry (Academic Publishing, New
-York, New York). Since
The invention is illustrated in more detail by the examples below.Example 1 CaF₂300nm and Tm-doped BaYY
bF₈Of 300 nm is Ga oriented in the (100) direction
Sequentially at 500 ° C by e-beam evaporation on As single crystal
Was deposited. The sample surface is glossy and smooth
It was The standard 2-theta diffraction pattern of FIG. 4 obtained from the multilayer structure.
Turns are GaAs (200) & (400), CaF
₂(200) & (400), BaYYbF₈(220)
Only the diffraction peak of & (440) was shown. Half the maximum value
Full width of rocking curve (FWHM) at CaF₂(2
00) about 0.5 °, BaYYbF₈(110)
Was about 0.9 °. Input to sample surface
X-ray analysis at 1.5 ° is other than GaAs (311)
No peak was shown. Therefore CaF₂And BaYYb
F ₈Both are not only highly oriented, but CaF
₂And BaYYbF₈Epitaxially grown on GaAs
It also has good in-plane alignment with GaAs, which indicates it has been lengthened
It BaYYbF₈The good crystal quality of the film is about 0.24.
By ion channel analysis showing a small yield
It was further confirmed (Fig. 5). CaF₂And BaYYbF
₈The respective refractive indices of 1.43 and 1.54 are
Is known, a waveguide is formed. 647.
The film is up-converted by the induction with a 1 nm laser beam.
Fusion, resulting in UV, blue, and green radiation
Emitted. Pumped by 960 nm laser beam
UV, blue, green and red light was seen when it was lit.Example 2 A thin film of LiF with a thickness of 300 to 500 nm is (10
At 400 ° C on a GaAs single crystal oriented in the 0) direction
BaYYbF deposited and 300-500 nm thick
₈Layer is e-beam evaporated on LiF coated substrate
Deposited at 500 ° C. The sample surface is smooth
There was no feature. X-ray diffraction of FIG. 6 obtained from X-ray analysis
GaAs (200) & (400), LiF in the pattern
(200), BaYYbF₈(110) & (220)
Only the diffraction peak is shown. LiF and BaYYbF₈of
The respective refractive indices are 1.36 and 1.55
As known, a waveguide is formed. 647.1n
The film is up-converged by the laser beam of m.
Excitation, resulting in the emission of UV, blue and green radiation
And was pumped by a 960 nm laser beam
We could see UV, blue, green and red light.

[Brief description of drawings]

FIG. 1 is a schematic view showing one embodiment of the multilayer structure of the present invention.

FIG. 2 is a schematic diagram showing an alternative embodiment of the multilayer structure of the present invention.

FIG. 3 is a schematic diagram showing another alternative embodiment of the multilayer structure of the present invention.

4 is a diagram showing an X-ray diffraction pattern of the structure shown in FIG.

5 is an analysis beam of the structure shown in FIG.
FIG. 6 shows Rutherford backscatter at <100> direction incidence for aAs.

6 is a diagram showing an X-ray diffraction pattern of the structure shown in FIG.

[Explanation of symbols]

 10, 20, 30 Multilayer structure 11, 21, 31 Single crystal semiconductor substrate 13, 23, 33 Buffer layer 15, 25, 35 Upconversion fluoride film

Claims (1)

[Claims] 1. A multilayer structure comprising a single crystal semiconductor substrate; an epitaxial buffer layer overlaying the substrate; and an epitaxial fluoride outer film layer exhibiting upconversion excited by red or infrared irradiation.